Satin white-clay compositions and methods of manufacture

ABSTRACT

A method of making a paper coating pigment by forming a satin white in aqueous suspension, adding thereto a kaolinite and removing a major portion of the water from the aqueous suspension to form a free flowing powder.

United States Patent [1 1 Conley et al.

[ Apr. 8, 1975 1 SATIN WHITE-CLAY COMPOSITIONS AND METHODS OF MANUFACTURE [75] Inventors: Robert F. Conley, Scotch Plains,

N..].; Billy Reid Catherwood, Macon, Ga; Mary Kate Lloyd,

Westfield, NJ.

[73] Assignee: Georgia Kaolin Company, Elizabeth.

[22] Filed: June 7, 1972 [2]] Appl. No.: 260,547

Related US. Application Data [63] Continuation-impart of Ser. No. 721.955. April 17.

[52] US. Cl 106/306; 106/308 N [51] Int. Cl. C090 H02 [58] Field of Search 106/306. 72. 214, 308 N Primary E.raminerWinston A. Douglas Assistant E.\'anziner.l. V. Howard Attorney, Agent. or Firm-Buell, Blenko and Ziesenheim [57] ABSTRACT A method of making a paper coating pigment by forming a satin white in aqueous suspension, adding thereto a kaolinite and removing a major portion of the water from the aqueous suspension to form a free flowing powder.

5 Claims, 3 Drawing Figures 10 RPM Brookfleld Viscosity, en.

0.4% Dequast 70l Koolmite 30%, Sutln White SATIN WHITE-CLAY COMPOSITIONS AND METHODS OF MANUFACTURE such admixture is preferably about to 30 percent by weight of the mixture. Amounts of satin white above about 30 percent create viscosity problems both in manufacture and subsequent use. Amounts below 10 percent provide minimal improvement in the resulting coating colors. The invention will be more clearly set forth in the following detailed examples.

EXAMPLE 1 A satin white composition is formulated by slurrying 5 parts of high purity lime in 75 parts water at room temperature and thoroughly mixing. A second solution of 25 percent aluminum sulfate is made up, a volume corresponding to about a Al (SO .18 H O Ca(OH) Si0115 of kaolinite and adhesive along with other pigweight ratio of 1.50. The aluminum sulfate solution is ments usually of high refractive index, are roll or blade dd d l wl bout 30 minutes total) to the line solucoated Onto 2 o ng p p r Sheet and dried thereon tion, so the temperature of the mixture does not rise It has been observed that he presen of micr oids above about 32C. The precipitation is continued until in the dried coating improve certain optical properties, a pH of 1 1.9 is reached. Thereafter a starch suspension notably opacity and gloss, and to a lesser extent brightis added in an amount corresponding to 10 percent by ness and whiteness. One mode of introduction of conweight of the precipitated calcium alumino-sulfate, or trolled voids is by the use of certain acicular pigments about 1.35 parts dry starch based on lime formulation. in small concentrations. lt has been theorized that such Starch acts as a binder in the lfinished coating formulapigments take up space by brush pile configuration tion and its addition to satin white improves the rheoland slowly release water during the drying process and ogy somewhat, as well as acting as a dispersant in the thus introduce voids of a size related to the particle system. The amount of starch. used in this invention is length. preferably in the range of about 5 to 15 percent on the One such material is known in the trade as Satin weight of satin white where desired. It is not essential White, a calcium sulfo-aluminate of somewhat indefias an element to forming the composition of this invennite composition, but believed to be primarily 3 CaO- tion or to the method of manufacture. .Al O .3 CaSO .32 H O. Satin White, as now known in The precipitate is filtered under pressure to attain the trade, is produced by mixing a solution of calcium 20-25 percent solids. hydroxide with one of aluminum sulfate in stoichiometric proportions. The chief problem in the manufacture EXAMPLE 2 of satin white is stability it must be kept in water sus- A21 commercial coating grade kaolinite which had pension. usually at about 20-25 percent solids. It is well e n pre iously a flO CE fi e and dried recognized that drying satin white destroys it together a Particle SiZe M M) 1 8 formulated 111 with the useful optical properties it imparts. It is obabout p n solids n water wthout dispersantserved that the suspension is even degraded at temperatures above C. While 75-80 percent water may be 40 EXAMPLE 3 higher than necessary for its stability, the extremely To this Suspension of Clay from Example 2 was added thixotropic viscosity of satin white in water makes it the Satin white of Example 1 in a proportion Cong Completely impmetleal to handle at eollds higher than sponding to 70 parts dry kaolinite and 30 parts dry satin 25 p The hlgh Water cement Introduces f M white. The composite material was about 30 percent Commercial preblems- PP Costs are exorblmm solids. The slurry was divided into three parts. and pp is Prohibited where exposure to Cold Part A was dried as formulated in an oven at 50C. weather results. The latter problem arises because Overnight. freezing of the water in satin white also destroys the p B was vacuum filt d and Oven dried at 5 pigmentary characteristics. The extra" water in satin 50 overnight. While y dilute the Coating Composition and require Part C was spray dried in a Nichols Niro Utility spray additional y g time and Costs its removal dryer having an inlet gas temperature of 380C. and an We have found the Premlxing Of Satin White and outlet gas temperature of 135C. While this temperaolinite and drying thereafter gives rise to a handleable, ture i h hi h h the oven d i temperature powdery material whose properties are not only not de- 5s h Contact i i l a fe d generated but actually improved Over the freshly Properties of the various mixtures and components in mulated components. The amount of satin white in E l 3 are iv i T bl I Table l Formulated Brookfleld Viscosity. c.p. Sample Solids "/r 10 RPM RPM Satin White 23 (max.) 8.400 [.400 Kaolmite Clay 54 (max.) 288 67 (A) 709? K 30% S.W. 39 l0.000* (B) 39 10,000* (C 39 .680 476 (D) fresh 40 11,200 2,140

Oven dried samples could not be fully redispersed due to the presence of cemented aggregates.

It is apparent that Sample C is better. with respect to rheology, than B or A, and even better than a freshly formulated composite. Sample C is a free flowing, dryappearing powder containing about 5.0% moisture. All spray dried materials referred to later made by this general process contain 5% or less moisture and are also free flowing powders which show no degradation after several weeks aging.

The samples in Table 1, except for A and B, were formulated into standardized coating compositions and coated onto a standardized paper rawstock sheet. The optical properties of the finished sheets are given in Table ll.

TABLE 11 (a) FIG. 2 is a graph as in FIG. 1 using various concentrations of sodium hexametaphosphate; and

FIG. 3 is a graph as in FIG. 1 using various concentrations of sodium hexametaphosphate and amino tri (methyl phosphonic acid) [Monsantos product Dequest].

The composites predispersed with mixtures of sodium hexametaphosphate and organic phosphonates such as amino tri (methyl phospshonic acid) and the salts thereof show the lowest initial viscosities and maintain a low level for an extended period. Such properties are essential for commercial processing. In spray drying a slurry is pumped through fine nozzles and at- Optical Properties of Uncalendered Sheets Coating whiteness Weight Gloss. Brightness. lndex. Opacity. Sample lb./ream at 75 at 457 ma, /1 7r /1 Satin White 5 2.4 71.7 26.7 93.3 Kaolinite Clay 5 4.6 73.2 26.9 93.7 (C) 707: K6071 S.W. 4.5 3.0 75.3 22.3 95.5 (D) 7091 K 307! S.W. fresh 4.5 2.0 72.8 26.8 94.0

Reflectance difference. 700 m 400 my Reflectance difference at 530 mp. over white/black Table 11 (b) Optical Properties of Coated Sheets after Calendering* Gloss. Brightness whiteness Opacity. Sample 7c at 75 at 457 mu.% index, '71 71 Satin White 27.2 69.5 30.8 93.4 Kaolinite Clay 24.1 72.0 28.3 93.3 (C) 70% K-7 S.W. 25.0 72.9 25.5 94.9 (D) 70% K-30% S.W. fresh 21.0 71.2 28.7 93.4

Two nips at five psig EXAMPLE 4 Samples of 7030 blends respectively of kaolinite and satin white were formulated similarly to Example 3 with varying dispersants. Stability tests were performed using viscosity measurements as a criterion. The results are illustrated in the accompanying drawings in which:

H6. 1 is a graph of aging characteristics of 25% solid suspension using various dispersants;

omized in a hot air stream. A low viscosity and high solids are absolutely essential for economic operation of such dryers. Also, in commercial operation it is not always feasible to spray dry a slurry immediately upon its formulation. It is common practice to integrate many production batches into a holding tank to mini-- mize inconsistencies and to balance out equipment throughput rates. Consequently, the rheological stability of a slurry is of considerable importance.

EXAMPLE 5 Samples similar in composition and formulation as set forth in Example 4 were dried on the commercial spray dryer to evaluate the effect of the initial dispersant and spray drying on finished coating properties. Preparation was similar to Sample C except a minimum dispersant level was employed to achieve pumping requirements for the spray dryer. Coated sheets were prepared with a slight starch modification of those in Example 3. The results appear in Table Ill.

TABLE ill (a) Physical Properties of Predispersed & Spray Dried Formulations Brookfield Viscosity. Dispcrsing "/1 cps* 1 Sample Agent Solids pH* RPM 100 (E) 70% K309i S.W. none 39.7 9.6 4160 840 (F) 0.257: (NaPQtM 39.6 9.5 5200 848 (G) 0.2% (NaPQQ 39.2 9.5 4200 676 0.1% Na CO (H) 0.2% (NaPO l 40.8 9.6 6320 1136 0.27: amino tri (methyl phosphonic acid) (1) 8071 K-Z0'71 S.W. none 397 9.4 1920 440 (J) 0.25% (NaPO 39.6 9.4 2800 584 (K) 0.2% (NaPOfl 39.6 9.4 2400 496 0.171 NZQCOa (L) 0..17: (NuPOfl'; 39.4 9.6 2040 736 0.27: amino tri (methyl phosphonic acid) of finished coating formulation TABLE straight spray dried member (in both composite ratios) in almost all optical properties. Optical Properties of Coated Sheets after Calcndering* Coating Gloss Brightness EXAMPLE 6 W /2 at Wh't 1': O; Sample li 457 r m??? i f Coating colors were formulated similar to those in previous examples except that an amount of titanium dioxide corresponding to 6 percent of the satin white (6) 13.3 739 349 899 was included. Titanium dioxide is a common pigment 3O employed in paper coating because of its high refrac- (l) 5 12.6 74.3 34.5 90.5 I (J) 5 14,3 743 335 90b tive index and. hence, brightness and opacity manifest- (K) 5 14.2 75.0 33.3 91.0 ing capacity. The T10 was introduced via the satin (L) 5 white and spray dried in situ. The coating properties of '2 nips'tll s psig these formulations are given in Table IV.

TABLE IV (a) Optical Properties of Uncalendered Sheets Coating Weight Brightness Whitness Sample Dispersant lb/ream at 457 my. 7: lndexf/r Opacity/.7:

(M) Satin White 6 75.4 30.8 90.5 (N) Kaolinite 6 74.1 34.4 91.1 (0) 7071 K307: S.W. none 6 75.7 30.9 91.2 (P) 70% K-307r S.W. 0.2% amino tri (methyl phosphonic acid) 6 76.2 29.6 91.9 0.2% (NaPO (O) 70% 14-30% S.W. 0.371 NH OH 6 75.5 31 2 91.5 (R) 70% 16307 S.W.' 0.3'71 Na P O; 6 75.2 31.6 90.8 (S) 80% K-ZOZ S.W." none 6 75.4 31.0 91.6 (T) 8071 K-207z S.W." 0.2% (NaPOah; 6.3 75.9 29.9 91.4

0.1% Na- .CO (U) 80% K-20'7l S.W. 0.2'71 amino tri (methyl phosphonic acid) 6 76.6 27.8 92.5

0.2% (NaPO added prior to spray drying actual pigment composition: kaolinite 66.892. satin white 28.69%. TiO 1.791 oxidized starch 2.90 "0.2% amino tri (methyl phosphonic acid) 0.27: (NaPO L added to coating formulation after spray drying actual pigment composition: Kaolinite 77.6%. satin white 19.492. TiO l. l'7i. starch =l.98

A comparison of physical properties in Table 111((1) TABLE W (b) shows that the predispersion. while reducing viscosity O tical Pr) rties of Coated Sheets after C alenderin for the spray-dryer feed (FIG. 1). results in a slight 1np g crease in finished formulation (coating color) viscosity. rGloss o Brightness whiteness Opacity While any viscosity increase is counter to good coating Sample 75 at 457 Index practice, this amount is not beyond the compensation (M) 391) 7 3(4 901 capacity of commercial coating machines. Of even 31% greater importance is the viscosity comparison of sam- (P) 5: 11 ples F, G. and H with D, a formulation whose viscosity is impracticauy high (5) 16:8 7411 35:5 91:0 The optical properties in Table 111(b) show an even (T) 16.4 74.7 32,0 913 greater advantage of predispersion in the spray drying (U) 751) 3L0 9L9 operation. All predispersed samples are better than the flips. 5 mg While dispersion prior to spray drying with tetrasodium pyrophosphate or sodium hexametaphosphatesodium carbonate yields a material having improved optical coating properties. the superiority in optical properties, obtained by predispersion with mixtures of sodium hexametaphosphate and amino tri (methyl phosphonic acid) is clearly evident.

In the foregoing specification we have set out certain preferred practices and embodiments of our invention, however, it will be understood that this invention may be otherwise embodied within the scope of the following claims.

We claim:

1. The method of producing an improved dry particulate coating pigment containing satin white and kaolin which after drying may subsequently be made up into aqueous coating compositions comprising the steps of:

a. forming a satin white composition in aqueous suspension;

b. adding a kaolinite and a sufficient amount of 7 amino tri (methylphosphonic acid) and salts thereof to disperse said clay to said aqueous suspension of satin white in sufficient amount to form LII a mixture containing about 10 to 30 percent by weight of satin white, and

c. removing water from the aqueous suspension to form a free flowing powder.

2. The method as claimed in claim 1 wherein the kaolinite is added as an aqueous suspension.

3. The method as claimed in claim 1 wherein the clay is predispersed with a sufficient amount of amino tri (methylphosphonic acid) to disperse the clay in said aqueous suspension.

4. The method as claimed in claim 1 wherein the water is removed by spray drying to a level of about 5%.

5. A dry particulate composition suitable for subsequent formulation in paper coating colors comprising a co-dried mixture of satin white and kaolinite of about 5% moisture content having added thereto a sufficient amount of a member from the group consisting of amino tri (methylphosphonic acid), salts thereof and mixtures of said acid and salts to provide dispersion of the solids in aqueous suspension. 

1. THE METHOD OF PRODUCING AN IMPROVED DRY PARTICULATE COATING PIGMENT CONTAINING SATIN WHITE AND KAOLIN WHICH AFTER DRYING MAY SUBSEQUENTLY BE MADE UP INTO AQUEOUS COATING COMPOSITION COMPRISING THE STEP OF: A. FORMING A SATIN WHITE COMPOSITION IN AQUEOUS SUSPENSION, B. ADDING A KAOLINITE AND A SUFFICIENT AMOUNT OF AMINO TRI(METHYLPHOSPHONIC ACID) AND SALTS THEREOF TO DISPERSE SAID CLAY TO SAID AQUEOUS SUSPENSION OF SATIN WHITE IN SUFFICIENT AMOUNT TO FORM A MIXTURE CONTAINING ABOUT 10 TO 30 PERCENT BY WEIGHT OF SATIN WHITE, AND C. REMOVING WATER FROM THE AQUEOUS SUSPENSION TO FORM A FREE FLOWING POWDER.
 2. The method as claimed in claim 1 wherein the kaolinite is added as an aqueous suspension.
 3. The method as claimed in claim 1 wherein the clay is predispersed with a sufficient amount of amino tri (methylphosphonic acid) to disperse the clay in said aqueous suspension.
 4. The method as claimed in claim 1 wherein the water is removed by spray drying to a level of about 5%.
 5. A dry particulate composition suitable for subsequent formulation in paper coating colors comprising a co-dried mixture of satin white and kaolinite of about 5% moisture content having added thereto a sufficient amount of a member from the group consisting of amino tri (methylphosphonic acid), salts thereof and mixtures of said acid and salts to provide dispersion of the solids in aqueous suspension. 